This invention relates to a device for operating an arm of an automatic operating machine such as an industrial robot, and is intended to provide an arm operating device, in the arm of which tensioning means is provided to maintain the optimum tension is applied to the arm by means of wrapping power transmission belts and transmission rods to smoothly bend the arm.
In general, in an automatic operating machine, its arm is frequently bent or stretched to perform various operations. For intance, in bending or twisting the arm of a robot, it is necessary to turn a bending arm which is pivotally secured to its supporting arm through a predetermined angle. This will be described with reference to FIG. 3. A bending arm 32 which sometimes takes the form of a "wrist" is provided at one end portion of a supporting arm 31. The bending arm 32 has a rotating shaft 33 to which a link plate 34 is fixedly secured. Another link plate 35 is provided on the other end portion of the supporting arm 31. The link plate 35 is coupled to the link plate 34 by means of link rods 36, so that the link plate 34 turns as the link plate 35 is turned, thereby to move (turn) the bending arm 32. In FIG. 3, reference numeral 37 designates a driving shaft to which the link plate 35 is fixedly secured.
In another example of the conventional arm operating device, chain wheels are used instead of the link plates 34 and 35, and a chain, instead of the link rods 36, is laid over the chain wheels.
However, such a conventional device is disadvantageous in that the operation of the driven side is delayed because of the play of the link mechanism or the elongation of the chain, aas a result of which the amount of operation is varied. Especially in the device for transmitting driving power by the chain, the longer the length of the chain, the greater the effect of elongation of the chain. That is, as shown in FIG. 4, the chain is vertically vibrated with an amplitude .delta. depending on the position of the sprocket. This is especially undesirable in the case where the position of the wrist which is moved is detected by a dog secured to the chain, because the dog is vibrated with the chain, which vibration varies the operating position of the dog. Furthermore, if the chain is twisted by that vibration, then the operation thereof becomes unstable.